The main objective of this project is to define Na-Ca2 ion interaction during the activation by vasoactive agents (norepinephrine, prostaglandins, and angiotensin) of the rat aortae and to investigate how these interactions are altered during spontaneous hypertension. We intend to delineate the effects of Na ion and hypertension on phasic and tonic components of norepinephrine-induced contraction. These then will be correlated with measurements of intracellular Ca2 ion release and Ca2 ion influx. The effects of alterations in (Ca2 ion norepinephrine-induced contraction and associated Ca2 ion fluxes will also be studied in rat aortae from spontaneously hypertensive rats (SHR) and normotensive rats. The Na-Ca2 ion interactions will be further studied by varying both (Na ion)o and (Ca2 ion)o simultaneously but keeping the ratio of (Na ion)o2/(Ca2 ion)o constant. We further propose to investigate the influence of Na ion and hypertension on the ATP stimulated Ca2 ion extrusion mechanism operative in smooth muscle for maintaining Ca2 ion homeostasis. Lastly, we intend to investigate the mechanisms of Ca2 ion minus cAMP interrelationship in vascular smooth muscle and the influence of Na ion and hypertension on the cAMP system. This will be investigated by studying the effects of (Ca2 ion)o, (Na ion)o and hypertension on control and agonist-induced increases in cAMP in rat aortae.